Spark Plug - dual spark vs single spark

basically..none..the idea is that its easier to fire..but in reality, as long as the ignition system is in good shape, and you have decent compression..single plug will do the trick fine...over the years, the car industry has played with dual plugs..mostly to help with emissions..(helps make a complete burn in a few cylinder designs where flame travel is an issue), other wise the only advantage for performance would be a top fueler..they are dumping so much fuel into the chambers they can drown the spark out..so a second plug is just a backup to make sure the cylinder ignites when its supposed to...I used to run a big block chevy race motor that dumped 2 500 hp nitrous kits into it on the starting line..never had an issue with drowning a plug out...(motor had a static 15.5 compression ratio as well)...

basically..longer wear less chance of fouling on a lower voltage system.
some COP high voltage systems the plugs may be charged and fire from tang to electrode (backwards) and hell it's wasted space otherwise why not use it?